Can a gunsmith diagnose accuracy issues?

[Cinders]

Hi all!

I'm still at it with my .308, trying to figure out a weird split pattern I'm getting.  Had to take a break during the Great Ammo Shortage of 'ought 20.

Also just found out my Timney trigger is defective 😞  So working on replacing that.

I'm getting a little fed up trying to find the problem with my rifle, it's a slow process of trying to borrow parts or to get to the range (or get ammo).  Would a gunsmith be able to diagnose my rifle?  It could be the barrel, the gas block, the compensator (swapped scope/mount out, roughly the same split pattern as before).

Thanks!

[jtallen83]

Which Gunsmith?

Gonna throw a link up here to your previous thread..... then I'll read it 

 

[shooterrex]

Did you ever try another scope and mount? I also had a build showing erratic groups. Gas block was touching the rail .

[Cinders]

Thanks for linking that!

Yeah, I tried a better scope with a different mount and the grouping got a little worse but with the same pattern (2 tight groups left and right of the aim point).

I did read your gas block reference, Rex, and I'm wondering if I can just run it by a real expert who can give me a more definite answer.  It is a process to get to a range (and find ammo), so I'm not so keen on slowly trying out a scope swap, removing compensator, re-torque barrel, taking apart gas block to see if I can figure out if it was touching something.

 

Also, good question: which gunsmith?  I'm asking is if this is even a thing to approach a gunsmith about.  

[Belt Fed]

If something is off on your rifle a good gunsmith should be able to find it. You should be able to just look at your gas block inside the rail and see it it's touching.

[shooterrex]

A gunsmith is going to have to do a lot of the same things you can do. Take the rail off. That will eliminate anything touching the gas block or barrel. Set the magazine on a sand bag and shoot it at 25 yds or so.

Just change 1 thing at a time.

A gunsmith is going to have to take it to the range and shoot it too.

[DustBuster]

On 6/10/2021 at 4:28 PM, shooterrex said:

Did you ever try another scope and mount? I also had a build showing erratic groups. Gas block was touching the rail .

I also have been seeing bad groups... today they were split... I made some previous posts about my shooting and grouping... Asking everybody about rings, scopes, ammo and brass, as well as my gas block.  It is, as Shooter Rex’s once was, about a business card clearance from the inside of handgaurd.  I did notice slight markings inside the handgaurd before, but today after closer inspection, I’m sure it is rubbing when the barrel harmonically whips.  I am going to tear it off this weekend and look at the gas port, and either reinstall a non-adjustable one with more clearance or grind some material off.  I definetely also had at least one distinct split group today...

[DustBuster]

Here is the most distinct split.  Reload ammo, same cases.  Pretty rock solid prone position.  I think it’s my gas block rubbing and it could be yours too, Cinders.

[98Z5V]

23 hours ago, Cinders said:

Also, good question: which gunsmith?  I'm asking is if this is even a thing to approach a gunsmith about.  

The only gunsmith I'd trust to diagnose an AR would be ADCO Firearms.  You'll have to call on the phone, and explain the situation - but there is no better commercial AR Gunsmith than ADCO.

https://adcofirearms.com/

[Cinders]

Thanks, 98Z!

 

Yeah, Dust, that looks pretty similar.  Mine are split a little more, but very tight groups in 2 distinct places, rather than a looser grouping.

[Cliff R]

Have you taken the human factor out of the equation?.....FWIW......Cliff

[Magwa]

1st question what ammo are you using that has to be the first look to then look for other issues but if it is garbage in it is garbage out...

[mtrmn]

I have seen this discussed on other forums and it seemed to be narrowed down, in at least one case, to be dependent on which side of the magazine the round came from. If firing from a full mag, rounds 1,3,5 had about the same POI and rounds 2,4, had a different POI. This possibility could be eliminated by only loading one rd in the mag at a time so that every shot originated from the same side of the mag. If the split grouping went away then that would be the likely cause. I don't know if or how the problem ever got fixed however.

[unforgiven]

You could strap down the rifle taking you out of the equation.

[98Z5V]

10 hours ago, mtrmn said:

I have seen this discussed on other forums and it seemed to be narrowed down, in at least one case, to be dependent on which side of the magazine the round came from. If firing from a full mag, rounds 1,3,5 had about the same POI and rounds 2,4, had a different POI. This possibility could be eliminated by only loading one rd in the mag at a time so that every shot originated from the same side of the mag. If the split grouping went away then that would be the likely cause. I don't know if or how the problem ever got fixed however.

That would definitely be because of the ejector...   Rounds feeding from the right side of the mag have to make that jump when chambering, because the ejector is on the left side of the bolt face.  Square-faced ejectors are the worst offenders causing this, especially in the large-frame ARs.

[mtrmn]

6 hours ago, 98Z5V said:

That would definitely be because of the ejector...   Rounds feeding from the right side of the mag have to make that jump when chambering, because the ejector is on the left side of the bolt face.  Square-faced ejectors are the worst offenders causing this, especially in the large-frame ARs.

Simple enough. Now I understand more about the reasons behind the round ejectors.

[98Z5V]

15 hours ago, mtrmn said:

Simple enough. Now I understand more about the reasons behind the round ejectors.

Exactly so.